<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <nav id="menu">
        <ul>
          <li>
            <a href="#" data-id="0">菜单1</a>
          </li>
          <li>
            <a href="#" data-id="1">菜单2</a>
          </li>
          <li>
            <a href="#" data-id="2">菜单3</a>
          </li>
        </ul>
  
        <div>
          <ul style="display: none">
            <li><a href="#">子菜单1-1</a></li>
            <li><a href="#">子菜单1-2</a></li>
          </ul>
          <ul style="display: none">
            <li><a href="#">子菜单2-1</a></li>
            <li><a href="#">子菜单2-2</a></li>
          </ul>
          <ul style="display: none">
            <li><a href="#">子菜单3-1</a></li>
            <li><a href="#">子菜单3-2</a></li>
          </ul>
        </div>
      </nav>

      <script>
        const ul=document.querySelector('#menu ul')
        const divUl=document.querySelectorAll('div ul')
        ul.addEventListener('click',function(e){
            // console.log(e.target.dataset.id);
            // console.log(e.target);
            if(e.target.tagName==='A'){
                const index= divUl[e.target.dataset.id]

                index.style.display= index.style.display==='block'?'none':'block'

                // if(index.style.display==='block'){
                //     index.style.display='none'
                // }else{index.style.display='block'}
                
            }
        })
      </script>
</body>
</html>